Broadcast and multicast routing A superb presentation from Joakim Lundmark and Martin Neuman

What is broadcasting and multicasting? Broadcasting ◦ Send to every user in a network Multicasting ◦ Send to specific users in a network

Broadcasting routing N-way-unicasting ◦ Most straightforward way to send a broadcast packet, to each destination is to make N copies, one for every user. And then send one to each user. ◦ Drawback: use a lot of bandwidth for one line.

Broadcasting routing Network duplication ◦ Using the network to create and distribute the copies. ◦ Flooding, sending to all neighbors in the network.

Broadcasting routing: Flooding Uncontrolled flooding ◦ A fatal flaw with flooding.  All nodes have two neighbors: Will broadcast packages indefinitely.  More then two neighbors: Will create a broadcast storm.

Broadcasting routing: Flooding Controlled flooding ◦ SNCF(Sequence-number-controlled flooding)  Every sender node puts its address and broadcast sequence-number in the broadcast packet.  Every node has a memory of the address and number of each packet it has duplicated and sent.  If it receives a packet in the memory it drops the packet. If not it forward-copy it to its neighbors.

Broadcasting routing: Flooding Controlled flooding ◦ RPF (Reverse path forwarding)  Only sends packet forward if it is received from the next node in the shortest path back to the sender.

Spanning-Tree Broadcast  Limits number of sent packets.  Creates a path for each node to forward received packets. A so called minimum spanning-tree.  This is done by routing algorithms. Broadcasting routing

Creating a center based spanning-tree  A central node is defined.  Then all nodes sends a message at the same time towards the center node until they arrive at ether the center node or a node that’s already a part of the tree. Broadcasting routing

Spanning-Tree Broadcast

Specific receivers ◦ How to identify the receivers of a packet. ◦ How to address a packet sent to these receivers. ◦ You can not have all the addresses in the packet because it would be to big. ◦ A multicast packet is sent by address indirection.  A single identifier for all the receivers.  This is done by a multicast group. Multicasting

Managing a group ◦ IGMP(Internet group management protocol). ◦ Provides the means for a host to inform the router that it wants to join a multicast group. ◦ It has 3 message types, used for management of the group.  Membership_QueryFor joining the group  Membership_ReportFor acknowledgements  Leave_GroupFor leaving the group Multicasting

Multicasting routing using a group-shared tree. ◦ Similar to the spanning-tree broadcast. ◦ May use nodes not in the group to “jump” between different parts of the group. Multicasting routing algorithms

Multicasting routing using a source-based tree ◦ Using a RPF(reverse path forwarding) algorithm each node gets its own spanning tree. ◦ This is better when many users wants to communicate with many users. Multicasting routing algorithms

Questions?